TolR

Structure
TolR is a bitopic protein located in the inner membrane and consists of three domains: domain I (from residues 1 to 43 and including the transmembrane domain between residues 23 to 43), domain II and domain III from residues 117 to 142. Domains II and III have the ability to dimerize, but unlike domains I and III, domain II is poorly conserved.

Domain III has been suggested to form an amphiphilic α-helix, which play an essential role in the functional assembly of the Tol complex.

Function
TolR has been shown to exhibit several functions :
 * 1) Interactions with other Tol proteins: Domain I is important for the interactions between TolA and TolQ, as deletion of this domain resulted in no cross-linkages formed between these proteins .  Domain III of TolR has also been shown to be involved in the TolQ-TolR interaction, but not directly linked .  However, even when deleted there is still cross linking between TolR and TolQ showing that domain III does not affect the interaction between the two proteins, but could instead affect the function of TolR .  As domain III has not been shown to interact directly with TolA or TolQ, the function of TolR could be affected indirectly by domain III altering the conformation of domain I thereby affecting the interaction between TolA/TolQ-TolR.
 * 2) Colicin A import
 * 3) Maintaining cell envelope integrity